The purpose of the project is to clone and characterize novel chemokine receptors in activated lymphocytes. Chemokines are members of a family of more than thirty human cytokines whose best described activities are as chemotactic factors for leukocytes and that act through receptors that are members of the G protein coupled receptor superfamily. Chemokines and their receptors are increasingly recognized as important in the trafficking of lymphocytes in immune and inflammatory responses as well as other aspects of lymphocyte physiology. Because lymphocytes are important in responses to infectious agents as well as in autoimmune diseases, inflammatory disorders, and transplant rejection, secreted factors and receptors that effect lymphocyte recruitment to tissue are potential targets for therapeutic interventions. Characterization of chemokine receptors on lymphocytes is of added medical relevance given the recent discoveries that chemokine receptors function as obligate co-receptors for HIV-1 entry, so that understanding these receptors may lead to novel therapies for preventing and treating HIV infection. Work during the last year has focused on three receptor:ligand groups that have been discovered and/or cloned and characterized in this laboratory, including the receptor CCR6 and its ligand MIP-3alpha, receptor CCR9A/B and its ligand TECK, and STRL33, an HIV/SIV coreceptor whose ligand is unknown. For CCR6, we found that although the receptor is expressed at equal levels, and binds MIP-3alpha equivalently on both resting and activated human B cells, CCR6 signals only on B cells after activation through surface antigen receptor. This suggests a novel mechanism for regulating chemokine receptor activity on lymphocytes. We cloned CCR9, showing that it was a receptor for TECK and we discovered two forms of the receptor that differed at their N-termini by twelve amino acids, calling the longer form CCR9A and the shorter CCR9B. We showed that the same cells express both forms and that the A form responds to and is desensitized by lower concentrations of TECK as compared with the B form. This provides a novel mechanism for cells to extend the range of concentrations of chemokine over which they can respond by producing alternative forms of a receptor from a single gene. For STRL33, we have pursued our investigations of the ability of HIV and SIV strains that use this coreceptor inefficiently to adapt to use it efficiently in vitro, and we have cloned and sequenced envelope glycoprotein (Env) genes from adapted viral strains and are characterizing the Envs to understand the molecular basis of the adaptation. Viral adaptation to alternative coreceptors may be important when anti-HIV therapies are introduced to block chemokine receptor-mediated viral entry.